1. Fields of the Invention
The present invention relates to a receiving and transmitting device for wireless transceivers, especially to a multiple-input multiple-output (MIMO) antenna used for WLAN operation. Good isolation is achieved by adjusting the distance between a radiating portion and a parasitic element of the present invention, without using any active or passive component.
2. Descriptions of Related Art
Nowadays a MIMO antenna is used to increase the isolation between antennas. Generally, the isolation is improved by increasing the distance between the two antennas, different polarization directions of the antennas, or adding isolation components on a dielectric substrate. For example, a band reject filter is disposed between two antennas so as to increase the isolation.
Although the isolation is improved by increasing the distance between the antennas, the size of the antenna is increased relatively. The size of the antenna is unable to be minimized. As to different polarization directions of the antennas, the radiation patterns generated are not symmetric. Moreover, there is still a dead angle of communication and this lead to poor communication quality. The arrangement of the band reject filter improves the isolation of antennas. But the volume of the antennas is unable to be reduced on the ground plane. The manufacturing cost and difficulty in circuit design are also increased.
Moreover, refer to Taiwanese Pat. Pub. No. 201117472, a dual-band printed circuit antenna for electronics is revealed. The antenna is a monopole antenna with a quarter wavelength (λ/4) in length at low frequency/three-quarter wavelength (3═/4) in length at high frequency so as to increase band width of high frequency signals. Moreover, the position of the feed point is selected under the condition that a plurality of antennas shares the same ground point. Thus the frequency band at high frequency has good isolation, radiation efficiency and band width.
Wireless devices have become essentials on our daily lives due to fast development of wireless communication technology. Thus various new antennas have been invented for fast catch-up of information at all times and all places. Even under terrible environment, the quality of signals received is good and the transmission speed is high.
Thus there is a need to provide a receiving and transmitting device for wireless transceivers with a simple structure for getting good isolation and avoiding interference problems when the two antennas are quite close to each other.